Conventionally, gold-silver alloy flash plating is formed at an outermost layer of a lead frame for a semiconductor device, to ensure a high resistance to corrosion. An example of such techniques is disclosed in Unexamined Japanese Patent Application Publication No. H11-008341.
FIG. 6 is a representation of a construction of a lead frame described in the above document. In the drawing, a lead frame 900 is formed by applying nickel plating 902, palladium plating 903, and gold-silver alloy flash plating 904 to a lead frame body 901 in this order. According to the document, the lead frame 900 having this construction exhibited an excellent corrosion resistance in a salt-spray test.
However, though this construction certainly has a high corrosion resistance, it has only a low light reflectance. This being so, especially when a semiconductor light-emitting element such as an LED is mounted on the lead frame to form a semiconductor light-emitting device, the lead frame cannot sufficiently reflect rear light of the light-emitting element, which impairs the luminous efficiency of the entire device.